Photoelectrophoretic and xerographic imaging processes employing triphenodioxazines as the electrically photosensitive component



y 1969 1.. WEINBERGER I 3, ,78

PHOTOELECTROPHORETIC AND XEROGRAPHIC IMAGING PROCESSES EMPLOYINGTRIPHENODIOXAZINES AS THE ELECTRICALLY PHOTOSENSITIVE COMPONENT FiledJan. 6. 1966 INVENTOR. LESTER WEINBERGER w/MM ATTORNEYS United StatesPatent Ofiice U.S. Cl. 204-181 7 Claims ABSTRACT OF THE DISCLOSURETriphenodioxazines are used as electrically photosensitive particles inphotoelectrophoretic imaging and as photoconductors in xerographicplates.

This invention relates in general to imaging methods. More specifically,the invention concerns the use of electrically photosensitive pigmentsin electrophotographic imaging systems.

There has been recently developed an electrophoretic imaging systemcapable of producing color images which utilize photoconductive pigmentparticles. This process is described in detail and claimed in copendingapplications Serial Numbers 384,737, now US Patent 3,384,565; 384,681,abandoned in favor of Ser. No. 655,023, now U.S. Patent 3,384,566, and384,680, abandoned in favor of Ser. No. 518,041, now US. Patent3,383,993, all filed July 23, 1964. In such an imaging system, variouscolored light absorbing particles are suspended in a non-conductiveliquid carrier. The suspension is placed between electrodes, subjectedto a potential difference and exposed to an image. As these steps arecompleted, selective particle migration takes place in imageconfiguration, providing a visible image at one or both of theelectrodes. An essential component of the system is the suspendedparticles which must be intensely colored pigments which areelectrically photosensitive and which apparently undergo a net change incharge polarity upon exposure to activating radiation, throughinteraction with one of the electrodes. The images are produced in colorbecause mixtures of two or more differently colored pigments which areeach sensitive only to light of a specific wave-length or narrow rangeof wave-lengths are used. Pigments used in this system must have bothintense pure colors and be highly photosensitive. The pigments of theprior art often lack the purity and brilliance of color, the high degreeof photosensitivity and/ or the preferred correlation between the peakspectral response and peak photosensitivity necessary for use in such asystem.

Another imaging system which utilizes electrically photosensitivematerial is the xerographic process as described in US. Patent 2,297,691to C. F. Carlson. Here, the photosensitive material must be an effectivephotoconductive insulator, i.e., must be capable of holding anelectrostatic charge in the dark and dissipating the charge to aconductive substrate when exposed to light. In the fundamental process,a base sheet of relatively low electrical resistance such as metal,paper, etc. having a photoconductive insulating surface coated thereon,is electrostatically charged in the dark. The charged coating is thenexposed to a light image. The charges leak off rapidly to the base sheetin proportion to the intensity of light to which the particular area isexposed, the charge being substantially retained in non-exposed areas,forming an electrostatic latent image. After exposure, the coating iscontacted with electrostatic marking particles in the dark. Theseparticles adhere to the areas where the electrostatic charge remains,forming a powder image corresponding 3,442,781 Patented May 6, 1969 tothe electrostatic latent image. Where the base sheet is relativelyinexpensive, such as paper, the image may be fixed directly to theplate, as by heat or solvent fusing. Alternatively, the powder image maybe transferred to a sheet of transfer material, such as paper, and fixedthereon.

Many phototsensitive materials useful in the xerographic process areknown in the art, e.g., vitreous selenium, sulfur, anthracene, zincoxide, polyvinyl carbazole. While several of these different materialsare in commercial use today, each has deficiencies in such areas asphotographic speed, spectral response, durability, reusability and costsuch that there is a continuing need for improved materials.

It is, therefore, an object of this invention to provide novelelectrophotographic imaging processes which overcome the above noteddeficiencies.

It is another object of this invention to provide novel electrophoreticimaging processes.

It is another object of this invention to provide novel xerographicimaging processes.

It is still another object of this invention to provide novelelectrophoretic imaging systems capable of reproducing color images.

It is still another object of this invention to provide novelxerographic plates having maximum spectral and photosensitive responsesin ranges other than those of prior plates.

The foregoing objects and others are accomplished in accordance withthis invention, fundamentally, by providing novel electrophotographicimaging processes utilizing compositions having the general formula:

1 13 12 11 2 /N\ am L ll which may be substituted at any available site.

The compositions of the above general formula belong to the class ofsubstituted and unsubstituted triphenodioxazines. These compounds arealso known as [1,41benzoxazino-[2,3-b1phenoxazines; 5,12dioxa-7,l4-diazapentacenes and triphendioxazines.

Of the compositions within the above general formula, those substitutedin the 6,13-positions with a halogen and in the 3,10 or 2,9 positionwith an alkoyl or arylol are preferred for use in electrophotographicimaging processes since they have especially pure color and are mosthighly photosensitive. Of these, the optimum compositions have beenfound to be 2,9-dibenzoyl-6,13-dichlorotriphenodioxazines and 2,9diacetyl 6,13 dichloro-triphenodioxazine. These have been found to givethe most desirable combination of color and photosensitivity inpolychromatic photoelectrophoretic imaging.

Since the shade or tone of the compositions and the spectral andphotosensitive responses vary slightly depending upon the substituentused, intermediate values of these variables may be obtained by mixingseveral of the different compositions.

The compositions within the general formula listed above, and mixturesthereof are especially useful as photosensitive pigment particles inelectrophoretic imaging processes. An exemplary electrophoretic imagingsystem is shown in the figure.

Referring now to the figure, there is seen a transparent electrodegenerally designated 1 which, in this exemplary instance, is made up ofa layer of optically transparent glass 2 overcoated with a thinoptically transparent layer 3 of tin oxide, commercially available underthe name NESA glass. This electrode will hereinafter be referred to asthe injecting electrode. Coated on the surface of injecting electrode 1is a thin layer 4 of finely divided photosensitive particles dispersedin an insulating liquid carrier. The term photosensitive, for thepurposes of this application, refers to the properties of a particlewhich, once attracted to the injecting electrode, will migrate away fromit under the influence of an applied electric field when it is exposedto actinic electromagnetic radiation. For a detailed theoreticalexplanation of the apparent mechanism of operation of the invention, seethe above mentioned copending applications Ser. Nos. 384,737, now US.Patent 3,384,565; 384,681, abandoned in favor of Ser. No. 655,023, nowUS. Patent 3,384,566, and 384,680, abandoned in favor of Ser. No.518,041, now US. Patent 3,383,993, the disclosures of which areincorporated herein by reference. Liquid suspension 4 may also contain asensitizer and/or a binder for the pigment particles which is at leastpartially soluble in the suspending or carrier liquid as will beexplained in greater detail below. Adjacent to the liquid suspension 4is a second electrode 5, hereinafter called the blocking electrode,which is connected to one side of the potential source 6 through aswitch 7. The opposite side of potential source 6 is connected to theinjecting electrode 1 so that when switch 7 is closed, an electric fieldis applied across the liquid suspension 4 between electrodes 1 and 5. Animage projector made up of a light source 8, a transparency 9, and alens 10 is provided to expose the dispersion 4 to a light image of theoriginal transparency 9 to be reproduced. Electrode 5 is made in theform of a roller having a conductive central core 11 connected to thepotential source 6. The core is covered with a layer of a blockingelectrode material 12, which may be Baryta paper. The pigment suspensionis exposed to the image to be reproduced while a potential is appliedacross the blocking and injecting electrodes by closing switch 7. Roller5 is caused to roll across the top surface of injecting electrode 1 withswitch 7 closed during the period of image exposure. This light exposurecauses exposed pigment particles originally attracted to electrode 1 tomigrate through the liquid and adhere to the surface of the blockingelectrode, leaving behind a pigment image on the injecting electrodesurface which is a duplicate of the original transparency 9. Afterexposure, the relatively volatile carrier liquid evaporates off, leavingbehind the pigment image. This pigment image may then be fixed in placeas, for example, by placing a lamination over its top surface or byvirtue of a dissolved binder material in the carrier liquid such asparafiin wax or other suitable binder that comes out of solution as thecarrier liquid evaporates. About 3% to 6% by weight of parafiin binderin the carrier has been found to produce good results. The carrierliquid itself may be paraffin wax or other suitable binder. In thealternative, the pigment image remaining on the injecting electrode maybe transferred to another surface and fixed thereon. The pigment imagemay be transferred, for example, by the methods described in copendingapplication, Ser. No. 459,860, filed May 28, 1965. As explained ingreater detail below, this system can produce either monochromatic orpolychromatic images depending upon the type and number of pigmentssuspended in the carrier liquid and the color of light to which thissuspension is exposed in the process.

Any suitable insulating liquid may be used as the carrier for thepigment particles in the system. Typical carrier liquids are decane,dodecane, N-tetradecane, paratfin, beeswax or other thermoplasticmaterials, Sohio Odorless Solvent 3440 (a kerosene fraction availablefrom Standard Oil Company of Ohio), and Isopar-G (a long chain saturatedaliphatic hydrocarbon available from Humble Oil Company of New Jersey).Good quality images have been produced with voltages ranging from 300 to5,000 volts in the apparatus of the figure.

In a monochromatic system, particles of a single composition aredispersed in the carrier liquid and exposed to a black-and-white image.A single color image results, corresponding to conventionalblack-and-white photog- 4 raphy. In a polychromatic system, theparticles are selected so that those of different colors respond todifferent wave-lengths in the visible spectrum corresponding to theirprincipal absorption bands. Also, the pigments should be selected sothat their spectral response curves do not have substantial overlap,thus allowing for color separation and subtractive multi-color imageformation. In a typical multi-color system, the particle dispersionshould include cyan colored particles sensitive mainly to red light,magenta particles sensitive mainly to green light and yellow coloredparticles sensitive mainl to blue light. When mixed together in acarrier liquid, these particles produce a black appearing liquid. Whenone or more of the particles are caused to migrate from base electrode11 toward an upper electrode, they leave behind particles which producea color equivalent to the color of the impinging light. Thus, forexample, red light exposure causes the cyan colored pigment to migrateleaving behind the magenta and yellow pigments which combine to producered in the final image. In the same manner, blue and green colors arereproduced by removal of yellow and magenta, respectively. When whitelight impinges upon the mix, all pigments migrate, leaving behind thecolor of the white or transparent substrate. No exposure leaves behindall pigments which combine to produce a black image. This is an idealtechnique of subtractive color imaging in that the particles are notonly each composed of a single component but, in addition, they performthe dual functions of final image colorant and photosensitive medium.

It has been found that the compounds of the general formula given aboveare surprisingly effective when used in either a single or multi-colorelectrophoretic imaging system. Their good spectral response and highphotosensitivity result in dense, brilliant images. The pigments here indisclosed have surprisingly good color separation and image densitycharacteristics.

Any suitable different colored photosensitive pigment particles havingthe desired spectral responses may be used with the pigments of thisinvention to form a pigment mlx in a carrier liquid for color imaging.From about 2 to about 10 percent pigment by weight have been found toproduce good results. The addition of small amounts (generally rangingfrom 0.5 to 5 mol percent) of electron donors or acceptors to thesuspensions may impart significant increases in system photosensitivity.

The following examples further specifically define the present inventionwith respect to the use of the compositions of the general formula givenabove in electrophoretic imaging processes. Parts and percentages are byweight unless otherwise indicated. The examples below are intended toillustrate various preferred embodiments of the electrophoretic imagingprocess of the present inventlon.

All of the following Examples I-XVI are carried out in an apparatus ofthe general type illustrated in the figure with the imaging mix 4 coatedon a NESA glass substrate through which exposure is made. The NESA glasssurface is connected in series with a switch, a potential source, andthe conductive center of a roller having a coating of Baryta paper onits surface. The roller is approximately 2 /2" in diameter and is movedacross the plate surface at about 1.45 centimeters per second. The plateemployed is roughly 3 inches square and is exposed with a lightintensity of 8,000 foot-candles as measured on the uncoated NESA glasssurface. Unless otherwise ndicated, 7 percent by weight of the indicatedpigments in each example are suspended in Sohio Odorless Solvent 3440and the magnitude of the applied potential is 2500 volts. All pigmentswhich have a relatively large particle size as received commercially oras made are ground in a ball mill for 48 hours to reduce their size toprovide a more stable dispersion which improves the resolution of thefinal images. The exposure is made with a 3200 K.

lamp through a 0.30 neutral density step wedge filter to measure thesensitivity of the suspensions to white light and then Wratten filters29, 6 1 and 47b are individually superimposed over the light source inseparate tests to measure the sensitivity :of the suspensions to red,green and blue light, respectively.

EXAMPLE I About 7 parts of 2,9-dibenzoyl-6,13-dichloro-triphenodioxazineis suspended in about 100 parts of Sohio Odorless Solvent 3440a Themixture is coated on the NESA glass substrate and a negative potentialis imposed on the roller electnode. The plate is exposed through aWratten 29 filter and the neutral density step we'dge filter, thusexposing the plate to red light. The results are tabulated in Table Ibelow.

EXAMPLE II A test is run as in Example I above, except that a Wratten 61filter is used in place of the Wratten 29 filter, thus exposing theplate to green light. The lated in Table I.

EXAMPLE III A test is run as in Example I above, except that a Wratten47b filter is used in place of the Wratten 29 filter, thus exposing theplate to blue light. The results are tabulated in Table I.

EXAMPLE IV A test is run as in Example I above, except that no colorfilter is used, thus exposing the plate to white light. The results aretabulated in Table I.

EXAMPLE V A test is run as in Example I above, except that the rollerpotential is positive rather than negative. As in Example I, a Wratten29 filter is used to expose the plate to red light. The results aretabulated in Table I.

EXAMPLE VI A test is run as in Example V above, except that a TheWratten 29 filter is used to expose the plate to red light. The resultsare tabulated in Table I.

EXAMPLEX A test is run as in Example IX above, except that a 5 Wratten61 filter is used in place of the Wratten 29 filter, thus exposing theplate to green light. See Table I for results.

EXAMPLE XI 10 A test is run as in Example IX above, except that aWratten 47b filter is used in place of the Wratten 29 filter, thusexposing the plate to blue light. See Table I for results.

1 EXAMPLE XII A test 1s run as in Example IX above, except that noWratten filter is used, thus exposing the plate to white. light. SeeTable I for results.

EXAMPLE XIII results are tabu- A test 1s run as in Example IX above,except that a positive rather than negative potential is imposed on theroller electrode. The plate is exposed through a Wratten 29 filter, thusexposing the plate to red light. See Table I for results.

EXAMPLE XIV A test is run as in Example XIII above, expect that aWratten 61 filter is used in place of the Wratten 29 filter, thusexposing the plate to green light. See Table I for 30 results.

EXAMPLE XV A test is run as in Example XIII above, except that a Wratten47b filter is used in place of the Wratten 29 filter,

thus exposing the plate to blue light. See Table I for results.

EXAMPLE XVI A test is run as in Example XIII above, except that noWratten filter is used, thus exposing the image to white light. SeeTable I for results.

TABLE I Roller Wratten Light Speed Example Potential Filter Color (t.e.)Gamma Dam Dmln I -2,500 None .j -2, 500 125 2. 0 1. s 0. 2 -2, 500 5002. 4 0. 6 -2, 500 2. 0 1.8 0. 2 +2, 500 None +2, 500 500 0. 3 1. 0 0. 6+2, 500 2,000 1.6 0.8 +2, 500 1, 000 0. 3 0. s -2, 500 1,000 0. 4 -2,500 300 3. 0 3. 0 0. 1 -2,500 500 0.1 -2, 500 250 a. 0 3. 0 0. 2 +2, 500None +2, 500 300 1. 7 7.0 0. 2 +2, 500 500 0.2 +2, 500 300 1. 7 7. 0 0.2

Wratten 61 filter is used in place of the Wratten 29 filter, thusexposing the plate to green light. See Table I for results.

EXAMPLE VII Wratten ifilter is used, thus exposing the plate to whitelight. See Table I for results.

EXAMPLE IX About 7 parts 2,9-diacetyl-6,13-dichloro-triphenodioxazine issuspended in about 100 parts Sohio Odorless Solvent 3440. The mixture istested as in Example I above.

The electrophoretie sensitivity of the various pigments to red, green,blue and white light is tested according to conventional photographicmethods and the results are recorded in Table I above. In the table, thefirst column lists the number of the test example. The second columngives the positive or negative electrical potential applied to theroller electrode in volts. The Wratten filters used in each examplebetween the light source and the NESA plate are listed in column three.The fourth column lists the color of the light which is permitted tofall on the NESA plate. The fifth column gives the photographic speed ofthe photosensitive mix in foot-candles. The photographic speed is theresult of a curve of optical density plotted against the logarithm ofexposure in foot candles; f.c. being 0.3 gamma toe speed and f.c. being0.3 gamma shoulder speed. Gamma, as listed in column 6, is a standardphotographic term referring to the slope of the above mentioned curve.The maximum and minimum reflection density produced are listed inColumns 7 and 8, respectively. In some instances, where the sensi tivityof the particular composition to the specific light color is low, gammaand D are not measurable. As shown by the above table, the testedpigments are sensitive, in an electrophoretic sense, to green lightprimarily. As can be seen, the pigments are essentially non-responsiveto red and blue light, having some slight response to blue light.

In each of Examples XVIIXXI below, a suspension including equal amountsof three different colored pigments is made up by dispersing thepigments in finely divided form in Sohio Odorless Solvent 3440 so thatthe pigments constitute about 8% by weight of the mixture. This mixturemay be referred to as a tri-mix. The mixtures are individually tested bycoating them on a NESA glass substrate and exposing them as in Example Iabove, except that a multicolor Kodachrome transparency is interposedbetween the light source and the plate instead of the neutral densityand Wratten filters. Thus, a multi-colored image is projected on theplate as the roller moves across the surface of the coated NESA glasssubstrate. A Baryta paper blocking electrode is employed and the rolleris held at a negative potential of about 2500 volts with respect to thesubstrate. The roller is passed over the substrate six times, beingcleaned after each pass. Potential application and exposure are bothcontinued during the entire period of the six passes by the roller.After completion of the six passes, the quality of the image left on thesubstrate is evaluated as to density and color separation.

EXAMPLE XVII The pigment suspension consists of a magenta pigment, 2,9dibenzoyl-6,13-dichloro-triphenodioxazine; a cyan pigment, Cyan GTNF,the beta form of copper pht-halocyanine, C.I. No. 74,160, available fromCollway Colors Company, and as a yellow pigment, 8,13-dioxodinaphtho(2,1-b,-2',3-d)-furan-6-carbox-m-chloroanilide, prepared by the methoddescribed in copending application Serial No. 421,377, filed December28, 1964. This tri-mix is exposed to a multi-colored image and producesa full color image of good density and color separation.

EXAMPLE XVIII The pigment suspension consists of a magenta pigment,2,9-diacetyl-6,13-dichloro-triphenodioxazine; a cyan pigment, Cyan Blue,3,3'-methoxy-4,4-diphenyl-bis(1"-azo- 2"-hydroxy-3"-naphthanilide), C.I.No. 21,180, available from Harmon Colors, and Algol Yellow GC, 1,2,5,6-di(C,C' diphenyl) thiazole anthraquinone, C.I. No. 67,300, availablefrom General Dye Stuff. This tri-mix is exposed to a multi-colored imageand produces a full color image of good density and excellent colorseparation.

EXAMPLE XIX The pigment suspension consists of a magenta pigment, 3,10dibenzoylamino 2,9 diisopropoxy-6,13-dichlorotriphenodioxazine; a cyanpigment, a polychloro-substituted copper phthalocyanine, C.I. No.74,260, from Imperial Color and Chemical Company, and a yellow pigmentIndofast Yellow Toner, flavanthrone, C.I. No. 70,600, available fromHarmon Colors. This tri-mix is exposed to multi-colored image andproduces a full color image of good density and color separation.

EXAMPLE XX The pigment suspension consists of a magenta pigment, 2,9dibenzoyl 6,13 dichloro-triphenodioxazine; a cyan pigment, Monolite FastBlue 6.8., the alpha form of metal free phthalocyanine, C.I. No. 74,100,available from the Arnold Hoffman Company, and a yellow pigment,1-cyano-2,3- 3'-nitro -phthaloyl-7,8-benzopyrrocoline, prepared asdescribed in copending application Serial No. 445,235, filed April 2,1965. This tri-mix is exposed to a multi-colored image and produces afull color image of satisfactory density and good separation.

EXAMPLE XXI The pigment suspension consists of a magenta, pigment, 2,9difuroyl 6,13 dichloro-triphenodioxazine; a cyan pigment, Cyan Blue XR,the alpha form of copper phthalocyanine, available from Collway Colors,and a yellow pigment 2,4-di-(1'-anthraquinonyl-amino)-6-(1"-pyrenyl)-s-triazine, prepared as described in copending applicationSerial No. 445,179, filed April 2, 1965. This tri-mix is exposed to amulti-colored image and produces a full color image of good density andcolor separation.

The compositions of the general formula given above are also useful inxerographic imaging systems. For use in such processes, xerographicplates may be produced by coating a relatively conductive substrate,e.g., aluminum or paper, with a dispersion of particles of thephotosensitive pigment of the above general formula in a resin binder.The pigment-resin layer may also be cast as a self-supporting film. Theplate formed may be both with or without an overcoating on thephotoconductive layer. As a third alternative to the above notedself-supporting layer and substrate supported layer, the photosensitivepigment-resin photoconductive layer may be used in the formation ofmultilayer sandwich configuration adjacent a dielectric layer, similarto that shown by Golovin et al., in the publication entitled A NewElectrophotographic Process, Effected by Means at Combined ElectretLayers, Doklady Akad. Nauk SSSR vol. 129, No. 5, pp. 1008-1011,November-December, 1959.

When it is desired to coat the pigmented resin film on a substrate,various supporting materials may be used. Suitable materials for thispurpose include aluminum, steel, brass, metalized or tin oxide coatedglass, semi-conductive plastics and resins, paper and other convenientmaterials.

Any suitable dielectric material may be used to overcoat thephotoconductive layer. A typical overcoating is bichromated shellac.

Any suitable organic hinder or resin may be used in combination with thepigment to prepare the photoconductive layer of this invention. In orderto be useful the resin used in the present invention should be moreresistive than about 10 and preefrably more than 10 ohms per centimeterunder the conditions of xerographic use. Typical resins includethermoplastics such as polyvinylchloride, polyvinylacetates,polyvinylidene chloride, polystyrene, polybutadiene, polymethacrylates,polyacrylics, polyacrilonitrile, silicone resins, chlorinated rubber,and mixtures and copolymers thereof where applicable; and thermosettingresins such as epoxy resins including halogenated epoxy and phenoxyresins, phenolics, epoxyphenolic copolymers, epoxy urea-formaldehydecopolymers, epoxy melamine-formaldehyde copolymers and mixtures thereofwhere applicable. Other typical resins are epoxy esters, vinyl epoxyresins, tall-oil modified epoxies, and mixtures thereof whereapplicable. In addition to the above noted binder materials, any othersuitable resin may be used, if desired. Also, other binders such asparaifin and mineral waxes may be used if desired.

The pigments may be incorporated in the dissolved or melted binder resinby any suitable means such as strong shear agitation, preferably withsimultaneous grinding. These include ball milling, roller milling, sandmilling, ultrasonic agitation, high-speed blending and any desirablecombination of these methods. Any suitable range of pigment-resin ratiosmay be used.

The pigment-resin-solvent slurry (or the pigment-resin melt) may beapplied to the conductive substrate by any of the well known painting orcoating methods, including spraying, flow coating, knife coating,electro-coating, Mayer bar drawdown, dip coating, reverse foil coating,etc. Spraying in an electric field may be preferred for the smoothestfinish and dip coating for convenience in the laboratory. The settingdrying and/or curing steps for these plates are generally similar tothose recommended for films of the particular binder used for otherpainting applications. For example, pigment-epoxy plates may be cured byadding a cross-linking agent and stoving according to approximately thesame schedule as other baking enamels made with the same resins andsimilar pigments for painting applications.

The thickness of the photoconductive films may be varied from about 1 toabout 100 microns, depending on their required individual purpose.Self-supporting films, for example, cannot usually be manufactured inthicknesses thinner than about 10 microns, and they are easiest tohandle and use in the 15 to 75 micron range. Coatings, on the otherhand, are preferably formed in the to 30 micron range. For certaincompositions and purposes, it is desirable to provide an overcoating;this should usually not exceed the thickness of the photoconductivecoating, and preferably not above one-quarter of the latter. Anysuitable overcoating material may be used, such as bichromated shellac.

The invention as it pertains to Xerographic imaging processes will befurther described with reference to the following examples, whichdescribe in detail various preferred embodiments of the presentinvention. Parts, ratios and percentages are by weight unless otherwisestated.

Xerographic plates for use as in the following examples are prepared asfollows: Mixtures using specific pigments and resin binders are preparedby ball milling the pigment or a solution of a resinous binder and oneor more $01-' vents until the pigment is well dispersed. This is done byadding the desired parts of the pigment to the desired parts of resinsolution in a suitable mixing vessel. A quantity of one-eighth steelballs are added and the vessel is rotated for approximately one-halfhour in order to obtain a homogeneous dispersion. The cooled slurry isapplied onto an aluminum substrate with a wire drawdown rod and forcedried in an oven for about 3 minutes at about 100 C. The coated sheetsare dark rested for about 1 hour and then tested.

In the following examples, plates are tested as follows. The plate ischarged negative by corona discharge to about 400 volts and exposed to alight and shadow image. The plate is cascade developed by the methoddescribed by Walkup in U.S. Patent 2,618,551. The powder image producedon the plate corresponds to the projected image. The developed image maybe then either fused to the plate or may be electrostaticallytransferred to a receiving sheet and there fused. Where the image istransferred, the plate may be then cleaned of residual toner and may bereused as by the above described process.

EXAMPLE XXII The Xerographic plate is prepared by initially mixing about2 parts of Lucite 2042, an ethylmethacrylate polymer available from E.I. duPont de Nemours and Co., about 18 parts benzene, and about 1 partof 2,9-dibenzoyl-6,l3-dichloro-triphenodioxazine. This mixture is coatedonto an aluminum substrate to a thickness of about 8 microns and cured.The plate is then charged, exposed for about 45 seconds to a light andshadow image using a Simmons Omega D3 enlarger equipped with a tungstenlight source operating at 2950" K. color temperature (illumination levelincident on the plate is 2.8 foot-candles as measured with a WestonIllumination Meter Model No. 756) and developed as above described. Theimage produced is heat fused directly onto the plate.

EXAMPLE XXIII The Xerographic plate is prepared by initially mixing abinder and a solvent as in Example XXII above with is electrostaticallyand shadow image using a Simmons Omega D3 enlarger equipped with atungsten light source operating at 2950 K. color temperature(illumination level incident on the plate is 2.8 foot-candles asmeasured with a Weston Illumination Meter Model No. 756) and developed.

EXAMPLE XXIV The Xerographic plate is prepared by initially mixing about3 parts of Lucite 2042 with about 100 parts benzene and about 10 partsof 3,l0-dibenzoylamino-2,9-diethoxy-6,13-diacylaminotriphenodioxazine.This mixture is coated onto an aluminum substrate to a thickness ofabout 8 microns and cured. The plate is then charged, ex posed for about45 seconds to a light and shadow image using a Simmons Omega D3 enlargerequipped with a tungsten light source operating at 2950 K. colortemperature (illumination level incident on the plate is 2.8 footcandlesas measured with a Weston Illumination Meter Model No. 756) anddeveloped. The image is heat fused onto the plate surface.

EXAMPLE XXV The Xerographic plate is prepared by initially mixing about10 parts Lucite 2042, with about parts benzene and about 2 parts3,10-dibenzoylamino-2,9-diisopropoxy- 6,I3-dichloro-triphenodioxazine.This mixture is coated onto an aluminum substrate to a thickness ofabout 10 microns and cured. The plate is then charged, exposed through afilm positive for about 30 seconds to a high intensity, long wave,ultraviolet lamp (1680 microwatts/ cm. of 3660 a.u. radiation at adistance of 18 inches) and developed. The powder image developed on theplate transferred to a receiving sheet by the method described bySchaffert in U.S. Patent 2,576,047 and heat fused. The image on thereceiving sheet corresponds to the contact exposed original. The plateis wiped clean of any residual toner and is reused as in the abovedescribed manner. The image on the receiving sheet corresponds to theoriginal.

EXAMPLE XXVI The Xerographic plate is prepared by initially mixing about10 parts Lucite 2042, with about 90 parts benzene and about 2 partstriphenodioxazine. The mixture is coated onto an aluminum substrate to athickness of about 10 microns and cured. The plate is then charged,contact exposed through a film positive for about 30 seconds to a highintensity, long wave, ultraviolet lamp (1680 microWatts/cm. of 3660 a.u.radiation at a distance of 18 inches) and developed. The image developedon the plate is electrostatically transferred to a receiving sheet andheat fused. The image on the receiving sheet corresponds to the contactexposed original. The plate is wiped clean of any residual toner and isreused as in the above described manner.

Although specific components and proportions have been described in theabove examples relating to electrophoretic, and Xerographic imagingsystems, other suitable materials, as listed above, may be used withsimilar results. In addition, other materials may be added to thepigment compositions or to the pigment-resin compositions to synergize,enhance or otherwise modify their properties. The pigment compositionsand/or the pigment-resin compositions of this invention may be dyesensitized, if desired, or may be mixed or otherwise combined with otherphotoconductors, both organic and inorganic.

Other modifications and ramifications of the present invention willoccur to those skilled in the art upon a reading of the presentdisclosure. These are intended to be included within the scope of thisinvention.

What is claimed is:

1. The method of electrophoretic imaging which comprises: (a) subjectinga layer of a particulate suspension to an applied electric field betweenat least two electrodes,

at least one of which is partially transparent; and, (b) simultaneouslyexposing said suspension to an image through said partially transparentelectrode with activating electromagnetic radiation whereby a pigmentimage made up of particles is formed on at least one of said electrodes,said suspension comprising a plurality of finely divided particles of atleast one color, at least some of said particles comprising aphotosensitive pigment selected from the group consisting of substitutedand unsubstituted triphenodioxazines.

2. The method of claim 1 wherein said photosensitive pigment has thegeneral formula:

wherein R is selected from the group consisting of alkoyl and aryloylradicals.

3. The method of claim 1 wherein said photosensitive pigment is2,9-dibenzoyl-6,13-dichloro-triphenodioxazine. 4. The method of claim 1wherein said photosensitive pigment is2,9-diacetoyl-6,13-dichlorotriphenodioxazine.

5. The method of claim 1 wherein said suspension comprises particles ofat least two different colors in an insulating carrier liquid, theparticles of each color comprising a photosensitive pigment whoseprincipal light absorption bands substantially coincides with itsprincipal photosensitive response.

6. The method of claim 1 wherein at least one of said electrodes is ablocking electrode.

7. The process for forming a latent xerographic image on aphotoconductive layer comprising a photoconductive pigment in an organicbinder, which comprises electrostatically charging said layer andexposing said layer to a pattern of activating electromagneticradiation; said photoconductive pigment comprising a compositionselected from the group consisting of substituted and unsubstitutedtriphenodioxazines.

References Cited UNITED STATES PATENTS 3,107,243 10/1963 Pugin et a1.260246 NORMAN G. TORCHIN, Primary Examiner.

JOHN C. COOPER III, Assistant Examiner.

US. Cl. X.R.

